Apparatus for the vapor deposition of metals



M y L 1951 4. G. opp/5 2,551,389

APPARATUS FOR THEVAP OR nizosi'rlon 0F METALS Filed June 10, 1947 2Sheets-Sheet l Jam/5: G. OLIVER 3nnentor May 1951 J. G. OLIVER APPARATUSFOR THE VAPOR DEPOSITION OF METALS Filed June 10, 1947 2 Sheets-Sheet 2Snventor OLIVE? qi k (Ittorneg Patented May 1, 1951 UNITED STATES IPATENT OFFICE APPARATUS FOR THE VAPOR DEPOSITION OF METALS James G.Oliver, Rosslyn Farms, Pa., assignor to Pittsburgh Plate Glass Company,Allegheny County, Pa., a corporation of Pennsylvania Application June10,1947, Serial No. 753,666 Claims. (01. 91-422) This invention relatesto apparatus for coating surfaces with a metal by thermally evaporatingthe metal in a vacuum.

Apparatus of this type presently is used to coat the reflecting surfacesof telescopic mirrors, Searchlight reflectors and other reflectivesurfaces, the optical properties of which must be carefully controlled.The coating is accomplished by supporting the coatin material and theobject to be coated within a chamber, creating a vacuum therein andevaporating the coating material by electrically heating it. 1

One objection to prior coating apparatus of this type is thatconsiderable time is required to create the vacuum. This is due to thefact that, in order to obtain a smooth coating of uniform thickness, itis necessary to support the coating material within the chamber at aconsiderable distance from the object, and consequently the size of thechambers and the volume of the atmosphere to be evacuated from them mustbe relatively large. A further ob jection is that the prior apparatusdoes not provide convenient access into the chamber for quick loadingand unloading of the object to be coated. This is due principally to themanner in which the chambers have been sealed by vacuum packing or thelike. Due to these and other objections which are known to those in thisart, the operations of the prior apparatus have been unnecessarily slowand inefficient.

The object of this invention is to provide an apparatus for depositingmetal on an object by thermal evaporation which may be quicklyevacuated, which provides convenient access for loading and unloadingand which substantially eliminates the necessity for special vacuumpacking.

According to the invention the object is coated in a vacuum chamberwhich includes a rigid end wall which forms a support for the object,another rigid end wall which forms a chamber head and a collapsible andexpandable side wall extending between the pair of end walls. Anelectric circuit enters the chamber through one of the chamber walls andincludes within the chamber means for vaporizing the coating materialwhen the chamber is expanded and mechanism is provided for moving one ofthe rigid end walls away from the other to expand the side wall and thusrarefy the interior of the chamber. With the interior rarefied, the coating material is evaporated to coat the object by energizing the circuit.

Although the vaporizing means may be an are between electrodes formed ofthe desired coating material, preferably it is an electric resistanceelement about which the coating material is wrapped. The element withthe material is mounted in the head of the chamber so that when the sidewall is expanded the coating material is positioned centrally of and ata proper distance from the object. Also, most suitably, the head is soshaped that, when the chamber is collapsed, only a small interior spaceis' left in the chamber, and a vacuum pump is 0011 nected into thisspace to quickly evacuate it.

The preferred embodiment of the invention is illustrated somewhatdiagrammatically in the accompanying drawings of which Fig. 1 is a planview of apparatus for simultaneously coating a plurality of objects;Fig. 2 is a vertical section on the line IIII of Fig. 1; Figs. 3 and 4are vertical sections through a collapsed and an expanded vacuumchamber, respectively; Fig. 5 is an enlarged section along the line VVof Fig. 4; and Figs. 6 and 7 are sections similar to Fig. 2 showing twodifferent operating positions of the apparatus.

The invention will be described with reference to depositing a coatingof metal such as chro-, mium on the concave surface of a glass mirror.However, it should be understood that the invention can be used forcoating other objects such as electrical capacitors, resistors, heaters,or even light cells and the like. ing material used depends upon thecharacteris-., tics which it is desired to obtain and can include othermaterials, such as silver, gold, aluminum, mercury, nickel, platinum,quartz, etc.

In the illustrative embodiment of the inven-. tion a mirror -I issuported on a support 2 which is provided with a mirror receiving recess3 and the top surface of the support is covered witha sheet 4 ofimpervious and resilient material such as an appropriate choroprenepolymer or other synthetic rubber which is resistant to heat and oils.

vacuum chamber 6 which is adapted to enclose the mirror in an air-tightseal so as to permit a vacuum to be created and the metal to beevaporated. The chamber is formed of a collapsible and expandable metalside wall or bellows l and a specially shaped head plate 3 which may beglass or metal as desired. The base of the chamber is formed by support2.

Also, the coat.

Referring to Figs. 3 and 4, the mechanism for coating a single mirrorincludes a On the' central portion of the head plate is formed a:vertical lug 9 to which is secured a pull rod H" which is connected topressure mechanism adapted both to raise and lower and to collapse andexpand the vacuum chamber. The pressure mechanism and its connectionswill be described later in conjunction with a complete machine forsimultaneously coating a plurality of mirrors. To the bottom of bellowsis secured, by brazing or the like, an air sealing plate l2 which iscarried by a cylindrical frame it surrounding the chamber. When thechamber is lowered, plate [2 contacts the resilient cover 4 of thesupport and pressure mechanism presses the plate into air-tightengagement with it so as to seal the mirror within the chamber. In orderto improve the air-tight seal, the lower surface of the plate [2 isprovided with circular sealing rings which press into the resilientcovering, or, if preferred, annular grooves can be formed thereon.

As shown in the drawings, head plate 8 is provided with 'a convex innersurface which, when the bellows is collapsed, closely contacts the majorportion of the concave surface of the mirror. A recess It is formed inthis convex surface and an electric heating element I5 is pivotallymounted in the recess. An operative form of such an element isillustrated in Fig. 5. The heating element there shown includes an arml6 about which is wrapped an electric resistance element in the form ofa filament I? and the coating material 3, which usually is in foil form,is wound about the filament. Arm !5 is pivoted on a pin i9 which issecured to opposite walls of the recess and a leaf spring 20, alsosecured to a wall of the recess, bears against the arm and normallyurges it outwardly of the recess to the position shown in Fig.4. Arm [6also is provided with extensions 2! which are adapted to abut the upperwall of the recess and limit the outward movement of the arm. Toenergize the filament, it is connected b-yconductors 22 to a source ofelectrical energy and the openings in the wall of the recess throughwhich the conductors pass are sealed by a glass seal 23. Also connectedinto the recess is standard type vacuum creating mechanism whichincludes a valve 24 and a line 25 leading to a vacuum pump. Valve 24 isseated by rotating handle 26 and, in its closed position, Fig. 4,atmosphere isprevented from seeping through the valve mechanism by meansof a seal 2! to which one end of a metal bellows 28 is attached, theother end of the bellows being secured to a rubber washer 29 which fitsover the valve seat.

In operation, the vacuum chamber and its associated parts are raisedfrom the support a sufiicient amount to permit the mirror to be placedin its supporting recess and. the chamber then is lowered into air-tightengagement with the support. Assuming the chamber to be expanded,pressure mechanism is operated to collapse it into the position shown inFig. 3. In such position the chambers head contacts the mirror and theheating element is pressed into recess I4. With the vacuum valve openthe pump is operated to evacuate the small volume of atmosphere which isin the recess and the collapsed bellows. It is to be noted that the timerequired for such evacuation is considerably shorter than it would be ifit were desired to evacuate the atmosphere of the usual chamber or belljar. Further, no diffusion or auxiliary pump is required to reduce thepressure to the degree necessary for evaporating the metal. When thevacuum has been reduced to about two hundred microns, the vacuum valveis closed thickness.

and pressure mechanism operated to expand the chamber to the positionshown in Fig. 4. The heating element springs out of the recess andplaces the metal to be vaporized in a position which preferably isradially equidistant from all points on the concave surface of themirror, so that when vaporized, the'metal spreads evenly over the mirrorand the coating is of uniform The heating elements filament then isenergized to vaporize the metal and coat the mirror. Preferably, thebellows are not fully expanded in Fig. 4 so that some bellows capacityis available for continuing the stroke during or immediately after themetallic evaporation.

Thus, additional bellows capacity may be necessary due to the evolutionof gases from the metal being evaporated from other interior surfaces ofthe chamber.

Figs. 1, 2, 6 and 7 illustrate apparatus for simultaneously coating aplurality of mirrors. In this particular machine, the support for themirrors is a circular table 39 in which are provided a plurality ofrecesses I l arranged in equally spaced radial positions. The table issupported on legs 3| and centrally secured to its bottom surface is acylinder 32 which is provided with pressure supply and exhaust lines 33and 34. A piston 36 is reciprocable in the cylinder by air or fluidpressure admitted through one or the other of lines 33 and 34 and apiston rod or arm 3? extends upwardly through the cylinder and projectsthrough a central opening in .table 30. The portion of the arm above thetable carries another air or fluid pressure cylinder 38 which also haspressure supply and exhaust lines 46 and 4| and a reciprocable piston42. Secured to this piston is a rod G3 which extends upwardly throughcylinder 38 and the upper end of rod 43 carries a plurality of radialspider arms 45 3 each of which carries at its outer end a pull rod IIwhich, as has been described, connect into the head plate of -a vacuumchamber. Preferably vacuum motor 4'! and pump 48 to which vacuum line 25connects are mounted centrally on the spider arms. The previouslymentioned vacuum chambers frame !3 is connected rigidly to the outsidewall of pressure cylinder 38 so that when arm 31 is reciprocated, thechambers are moved upwardly or downwardly.

The operation of this machine "is illustrated in Figs. 2, 6 and 7. Themachine shown in Fig. 2 is in its loading and unloading position, thechambers having been raised clear of table by admitting pressure throughpressure supply line 33 to raise piston rod or arm 37. It can be notedhere that each of the pairs of pressure supply and exhaust lines 333@and til-4i are connected to a four-way valve 44 which is of well-knownconstruction and which is controllable to admit the pressure througheither one of the lines of the pairs and simultaneously exhaust thepressure from the other one, and the valves, of course, are connected toa source of hydraulic or pneumatic pressure. After the machine isloaded, the vacuum chambers are lowered into contact with the table byadmitting pressure into cylinder 32 through line 3t. If the bellows arein an expanded condition they may be collapsed, so as to bring headplate 8 into contact with the mirrors by admitting pressure intocylinder 38 through line ll to lower only the spindle arms. Theatmosphere remaining in the chambers then is evacuated by pump 48 andwhen the pressure has been reduced the required amount, the chambers aresimultaneously expanded by admitting pressure into cylinder 38 throughline 48' to raise the spider arms. In this position, which isillustrated by Fig. '7, the metal is evaporated and the mirrors coatedin the manner previously described. The chambers then may be liftedclear of the table and the machine unloaded, reloaded and the cyclequickly repeated.

An important advantage of this invention is that, due to the speed andefficiency with which a plurality of mirrors can be coated, it is welladapted for commercial operations. Such speed results from the shortperiod required for obtaining the necessary vacuum and also from theefiiciency of the loading and unloading operations. The quick loading ismade possible bythe elimination of special vacuum packing, in place ofwhich the machine uses pressure mechanism to create the air seal. Also,in prior similar apparatusthere was a constant danger of contaminationfrom volatiles contained in the chamber and in the numerous mechanicalconnections through the chamber walls and this danger is substantiallyreduced by the invention. Also, by using a minimum of mechanicalconnections, the apparatus insures a better air seal for the chamber.

According to the provisions of the patent statutes, I have explained theprinciple and construction of my invention and have illustrated anddescribed what I now consider to represent its best embodiment. However,I desire to have it understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallyillustrated and described.

I claim:

1. Apparatus for coating a surface of an object by deposition thereon ofa material thermally evaporated in a vacuum, which comprises a bed platesurfaced with a layer of resilient material upon which an object to becoated may be supported, a collapsible and expandable bellows ofcircular configuration positioned to cover and surround an object whensupported in operative position on the resilient material, means forobtaining an air-tight seal between the lower edge of the bellows andthe bed plate, a closure secured to the upper portion of the bellows,means for collapsin and expanding the bellows, and means mounted withinthe bellows for vaporizing a coating material therein.

2. Apparatus for coating a surface of an object by deposition thereon ofa material thermally evaporated in a vacuum, which comprises a bed platesurfaced with a layer of resilient material upon which an object to becoated may be supported, a collapsible and expandable bellows ofcircular configuration positioned to cover and surround an object whensupported in operative position on the resilient material, means forobtaining an air-tight seal between the lower edge of the bellows andthe bed plate, a closure secured to the upper portion of the bellows,means for collapsing and expandin the bellows, means for evacuating thebellows, and means mounted within the bellows for vaporizing a coatingmaterial therein.

3. Apparatus for coating a surface of an object by deposition thereon ofa material thermally evaporated in a vacuum, which comprises a bed platesurfaced with a layer of resilient material upon which an object to becoated may be supported, a collapsible and expandable bellows ofcircular configuration positioned to cover and surround an object whensupported in operative position on the resilient material, means forobtaining an air-tight seal between the lower edge of the bellows andthe bed plate, a head plate secured to and closing the upper end of thebellows, an electric resistance element, for carrying coatin material tobe vaporized, pivotally mounted upon said head plate within saidbellows, means for energizing the electric resistance element toevaporate the coatin material, means for evacuating the bellows andmeans for collapsing and expanding the bellows.

4. Apparatus for coating a surface of an object by deposition thereon ofa material thermally evaporated in a vacuum, which comprises a bed platesurfaced with a layer of resilient material upon which an object to becoated may be supported, a sealing plate provided with a central openingof sufficient size to avoid contact with an object supported upon thelayer of resilient material, a cylindrical frame supporting said sealingplate and adapted for movement to and from said bed plate, a circularhead plate independently supported and adapted for verticallyreciprocating movement within the cylindrical frame, a collapsible andexpandable bellows of circular configuration extending between said headplate and said sealing plate and secured therebetween, means forevacuating the bellows and means carried upon the inner surface 'of thehead plate for vaporizing a coating material within the bellows.

5. Apparatus for coating a surface of an object by deposition thereon ofa material thermally evaporated in a vacuum, which comprises a bed platesurfaced with a layer of resilient material upon which an object to becoated may be supported, a sealing plate provided with a central openingof sufficient size to avoid contact with an object supported upon thelayer of resilient material, a cylindrical frame supporting said sealingplate and adapted for movement to and from said bed plate, a circularhead plate independently supported and adapted for verticallyreciprocating movement within the cylindrical frame, a collapsible andexpandable bellows of circular configuration extending between said headplate and said sealing plate and secured therebetween, an electricresistance element, for carrying coating material to be vaporized,pivotally mounted upon said head plate within the bellows, means forenergizing the electric resistance element to evaporate the coatingmaterial, and means for evacuating the bellows.

JAMES G. OLIVER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,151,457 Williams May 11, 19392,341,603 Dorn, et al Feb. 15, 1944

